1. Field of the Invention
The present invention relates to a plasma display panel (PDP) system (for example, plasma display), and particularly, to an apparatus for detecting average picture level applied to the PDP system.
2. Description of the Background Art
Generally, in a PDP system, an apparatus for detecting average picture level (APL) is mainly used for realizing a picture of high quality using Human's sight. Especially, Weber-Fechner principle shows that the human sight has higher brightness judgement, but has lower brightness judgement in dark area.
The above APL is a method for realizing gradation display visually at every frames as considering relation of data, which will be displayed on a screen, with neighboring pixels regardless of that the data is dark image data or bright image data, and aims to maintain power consumption constantly at every frames when the image is displayed on the screen. Also, the APL is defined as a numerical value obtained by averaging gradation levels of cells. For example, if black color is displayed on a full screen, then the APL is 0%, and if white highest gradation level (255) is displayed on the full screen, the APL is 100%. The APL of typical images is about 30˜40% in average.
FIG. 1 is a block diagram showing a structure of an APL detecting apparatus according to the conventional art.
As shown therein, the APL detecting apparatus according to the conventional art comprises: a red color data summing unit 11 for summing red color data corresponding to red colors among image data of one frame; a green color data summing unit 12 for summing green color data corresponding to green color among the image data; a blue color data summing unit 13 for summing blue color data corresponding to blue color among the image data; a multiplying unit 14 for multiplying summed red color data value by weight corresponding to size of red color pixel; a multiplying unit 15 for multiplying summed green color data value by weight corresponding to size of green color pixel; a multiplying unit 16 for multiplying summed blue color data value by weight corresponding to size of blue color pixel; a summing unit 17 for summing up the red, green and blue data values multiplied by the weight, averaging the summed red, green and blue color data values, and outputting the averaged data values; and an APL outputting unit 18 for outputting an APL value by multiplying the averaged data by a pre-decided gain for making 255 gradation. Herein, the image data of one frame corresponding to an input video signal comprises data corresponding to red, green and blue colors, and pixels of the PDP are controlled by the three colors data to display the image on the screen. In addition, the three-color data have maximum 255 gradation value. Hereinafter, operations of the APL detecting apparatus according to the conventional art will be described as follows.
First, the summing units 11˜13 sum the respective data corresponding to the red, green and blue color pixels among the image data of one frame, and output the summed red, green and blue color data to the multiplying units 14˜16.
The multiplying units 14˜16 multiply the sums of red, green and blue color data of video format (for example, 640×480 resolution) by weights corresponding to the sizes of red, green and blue color pixels in order to reflect affects according to the pixel sizes, and output the multiplied values to the summing unit 17. Herein, since the brightness and power consumption of the red, green and blue color pixels of the PDP are different from each other, the size of respective pixel may be changed in order to compensate the brightness and power consumption of the pixel.
After that, the summing unit 17 sums the red, green and blue color data values multiplied by the weights, averages the summed data values, and outputs the averaged value to the APL outputting unit 18 as an average value.
The APL outputting unit 18 multiplies the average value outputted from the summing unit 17 by gain value, which is set in advance for compensating error generated during calculating binary average value, to make the APL value maximum (100%) in case that the input data is the data representing only white color. Herein, the gain is a value which is set in advance in order to make the average value 255 gradation value.
However, according to the APL detecting apparatus of the conventional art, the average value outputted from the summing unit 17 is changed by characteristics of red, green and blue color pixels, sizes of the pixels and illuminating property of the pixel according to that the input video format (for example, resolution) is changed variously, and thereby the gain value should be controlled according to the change. However, it is difficult to control the gain value which is set in advance. That is, according to the PDP system of the conventional art, a panel having a structure suitable for the video format is fabricated, and sizes and color temperatures of respective red, green and blue color pixels are different from each other. Therefore, in calculating the APL value, the weights multiplied with the red, green and blue color data are different, and accordingly, the average value is also changed. Thus, a lot of gain values suitable for the average values are needed in one video format.
Also, in case that the APL value which is the final value outputs larger changing value than that of the input data, that is, input/output wave forms are non-linear, the screen can be flickered. For example, when error value of 1 bit is generated during the input video signal is converted into pixel-by-pixel digital image data, and flickering of PDP screen is shown remarkably.